Herbage, phosphorus, and nitrogen yields of winter-season forages on high-phosphorus soil
In climates where cool seasons can produce a forage crop, annual grasses and forbs can be used on dairies to recycle nutrients back to the animals and to phytoremediate soils high in P or N. In north-central Texas, on a Windthorst fine sandy loam (fine, mixed, thermic, Udic Paleustalf) with 250 mg P kg–1, an on-dairy trial measured yields of dry matter (DM), N, and P, as well as fiber fractions of five cool season legumes, six grasses, and two brassicas. Some grasses yielded >8 Mg herbage DM during high rainfall years, whereas the most productive legumes and brassicas could only match half that production. Because the soils were high in nitrate-N and plant-available P, concentrations of these were high in herbage, resulting in >150 kg N ha–1 yield in seven of the entries and >20 kg P in eight entries during a high-rainfall year. Potential for extracting, fixing, and sequestering N and P, combined with generally low fiber concentrations, indicated that some of these forages hold promise for nutrient recycling or phytoremediation of high-N or -P dairy soils with the added benefit of producing nutritious forage for the dairies.